The broad, long-term objective of the proposed randomized clinical trial is to evaluate the efficacy, moderators and mechanisms of change of two cognitive-behavioral aftercare treatments for alcohol and other drug (AOD) use disorders in preventing AOD relapse compared to standard aftercare (SA) offered in the community. The two cognitive-behavioral aftercare treatments are relapse prevention (RP;Daley &Marlatt, 2006) and Mindfulness-Based Relapse Prevention (MBRP), which integrates mindfulness meditation and RP aftercare components. The proposed research plan will address three specific aims. The first aim is to examine the efficacy of MBRP and RP compared to SA in preventing AOD relapse following intensive inpatient (IP) and outpatient (IOP) AOD treatment. Participants will be recruited from IP and IOP treatment and randomized to 8 weeks of MBRP, RP or SA. Treatment efficacy, as defined by reductions in AOD use and related consequences, will be evaluated at posttreatment and 3-, 6-, 9- and 12- month follow-up assessments. It is hypothesized that both MBRP and RP will result in significantly less AOD use and related consequences compared to SA. The second specific aim is to evaluate potential mediators of MBRP and RP treatment efficacy. It is proposed that the MBRP and RP interventions will be differentially effective in reducing AOD use and consequences based on the unique objectives of each treatment approach. It is therefore hypothesized that MBRP efficacy will be mediated by metacognitive processes, locus of control, mindfulness, thought suppression, ability to cope with craving and negative affect, experiential avoidance, emotion regulation and intensity of meditation practice. It is further hypothesized that RP efficacy will be mediated by negative affect, positive expectancies, self-efficacy and coping abilities. The final aim is to test potential moderators of treatment efficacy. It is hypothesized that participants with higher baseline levels of avoidant coping, experiential avoidance and lower levels of emotion regulation will benefit more from MBRP vs. RP treatments;whereas participants with lower self-efficacy and higher positive expectancies at baseline will benefit more from RP vs. MBRP treatments. In fulfilling these specific aims, the proposed research will address the NIDA mission for Stage II treatment research by examining the efficacy, moderators and differential mechanisms of change of various AOD aftercare treatments. PUBLIC HEALTH RELEVANCE: Given the high prevalence of alcohol and other drug (AOD) abuse in the general population and the high rates of relapse following AOD treatment, the proposed research will provide a valuable next step in evaluating the efficacy of two cognitive-behavioral treatments, relapse prevention and mindfulness-based relapse prevention, as aftercare treatments for AOD disorders in comparison to standard aftercare offered in the community. Further, the proposed research is designed to gain a better understanding of why these treatments work and for whom.